A flat flexible cable (FFC) is a common connecting wire between electric devices. It is advantageous to be easily and reversibly bent and stretched in a narrow and crowded space. For example, in a flatbed image scanner, the moving-around carriage module containing therein optical and photoelectric devices is connected with the circuit board through a flat flexible cable. Please refer to FIGS. 1A and 1B which are top and cross-sectional side views, respectively, schematically showing the connecting operation of a flat flexible cable in a flatbed image scanner. The flatbed image scanner 1 includes an upper cover (not shown) and a lower casing 10. In the lower casing 10, a carriage module 11 containing therein optical and photoelectric devices, a driving device consisting of a motor and gear set 121 and a rail set 122, a circuit board 13 including various electronic elements and electrically connected to a computer system 2 via a cable 16, and a flat flexible cable 14 connecting the carriage module 11 with the circuit board 13 are sealed under a transparent scanning platform 15. The carriage module 11 is moved by the motor and gear set 121 along the rail set 122 to pass by and scan a document or picture placed on the transparent scanning platform 15 so as to realize the image data of the document or picture.
Please refer to FIG. 2A which is a schematic cross-sectional diagram showing the structure of a conventional flat flexible cable. The flat flexible cable 14 includes a flexible copper foil 141, an insulating wrapper 142 made of a flexible plastic, and a strengthening plate 143 made of a rigid plastic. The insulating wrapper 142 surrounds the flexible copper foil 141 with two ends of the flexible copper foil 141 exposed for electric contact with the carriage module 11 and the circuit board 13, respectively. The strengthening plate 143 is mounted onto the end portion of the flat flexible cable 14 to facilitate the insertion of the exposed copper foil into the connecting slot (not shown) of the carriage module 11 or the circuit board 13. Further referring to FIG. 1B again, a portion 145 of the flat flexible cable 14 connecting to the circuit board 13 is fixed on the bottom of the lower casing 10, and another portion 146 connecting to the carriage module 11 is freely bent and stretched along with the movement of the carriage module 11.
During the movement of the carriage module 11, the flat flexible cable 14 keeps on electrically connecting the carriage module 11 with the circuit board 13 for signal transmission. The configuration of the flat flexible cable 14 changes all the time during the movement of the carriage module 11 along a scanning direction indicated by an arrow C. The distant end 144 of the flat flexible cable 14 from the carriage module 11, i.e. the U-turn portion, is likely to rise up to the inner surface of the transparent scanning platform 15, as shown in FIG. 2B, due to the flexible property thereof. Especially for an image scanner using a contact image sensor (CIS) as an image pickup device which requires close contact with the document on the transparent scanning platform 15, the flat flexible cable 14 generally keeps in contact with the inner surface of the transparent scanning platform 15 by a part thereof. For example, at a start position where the carriage module 11 is adjacent to the circuit board 13, the flat flexible cable 14 is bent to have a U-turn point at a position relative to the position A on the transparent scanning platform 15, as shown in the solid line of FIG. 1B. On the other hand, at a scanning position where the carriage module 11 moves away from the circuit board 13, the U-turn position shifts to a position B on the transparent scanning platform 15 along the scanning direction C, as indicated by the dotted line of FIG. 1B. As a result, abrasion is likely to occur due to the contact of the insulating wrapper 142 of the flat flexible cable 14 with the transparent scanning platform 15 and the movement of the contact point from the position A to the position B. In general, the insulating wrapper 142 is made of a thermoplastic plastic material and the transparent scanning platform 15 is made of glass. As known, a general thermoplastic plastic material has a smaller hardness than the hardness of the transparent scanning platform 15, so plastic chips may be generated due to the abrasion of the plastic flat flexible cable 14 and the glass scanning platform 15 so as to adversely affect the scanning quality.
Furthermore, in the above flatbed image scanner, the circuit board 13 is disposed on the bottom of the lower casing 10 and hard to be rearranged because of the physical connection to the carriage module 11 via the flat flexible cable 14. Therefore, the miniaturization of the image scanner, which is a trend of modern scanners, is difficult to be achieved.